Sligo, you probably have'nt been looking hard enough just checked EZY today, single fares, random days selected:
3rd March Monday LTN-GVA £22.50
3rd March Monday LTN-AMS £27:50
LGW-AMS £37:50
14th April Monday LTN-GVA £42:50
14th April Monday LTN-AMS £37:50
LGW-AMS £27:50
25th March Tuesday LTN-AMS £17:50
LGW-AMS £17:50
on line prices all taxes inc.
The earlier you book the better the chances of a very good deal, flexibility in your travel obviously helps too.
Also just for interest GNER (train) price single London to Retford 21 March 120 miles, £23:00.
So no great difficulty at all! Can't understand where the problem is
Edited to add LGW prices